FRIDAY, Oct. 30 (HealthDay News) -- Pregnant women head the list of people who should get H1N1 swine flu and seasonal flu shots, and four new studies highlight the benefits of vaccination for moms-to-be and their babies.

Bigger, healthier newborns, fewer preterm births and reduced rates of hospitalization top the findings, which are to be presented this week at the annual meeting of the Infectious Disease Society of America in Philadelphia.

In one study, U.S. researchers analyzed data on 6,410 births in Georgia and found that the risks of premature delivery and having a low birth-weight infant were significantly reduced among the 15% of women who received a flu shot during pregnancy.

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During the height of the flu season premature births among vaccinated women fell 70%, compared with unvaccinated women, Dr. Saad B. Omer, an assistant professor of global health and epidemiology at Emory University's Rollins School of Public Health, said during a news conference Thursday at which all four studies were discussed.

And the likelihood of having a small baby was reduced 70%, Omer added.

Similar positive results would likely be seen among women getting the H1N1 vaccine for swine flu, Omer said. Studies have found in previous flu pandemics that pregnant women were at risk for giving birth prematurely to underweight babies, he said.

Despite the benefits of seasonal flu vaccine, the rate of vaccination among pregnant women is "dismal," Omer said. Only about 25% of pregnant women are getting vaccinated, he said. He and his co-authors cited a need to publicize the benefits of vaccination in pregnancy.

In another report, Yale University School of Medicine researchers, led by Dr. Marietta Vazquez, an assistant professor of pediatrics, looked at the relationship between pregnant women who got flu shots and hospitalization rates for those infants.

The researchers found that the mother's flu shot during pregnancy was 78.9% effective in preventing her non-vaccinated infant from being hospitalized during the first year of life and 85.3% effective in preventing hospitalization from infancy to 6 months.

"These results will have a positive impact, not only on susceptible infants, but will prove to be cost- effective," Vazquez said. "If you think about this, we are talking about one vaccine protecting two individuals."

In another report, a team led by Dr. Mark C. Steinhoff, director of the Global Health Center at Cincinnati Children's Hospital Medical Center, looked at the relationship between flu shots and birth weight in Bangladesh.

Women who were vaccinated were 30% less likely to develop respiratory illness with fever, and those women had substantially heavier infants than unvaccinated women, the researchers found. The study confirmed that pregnant women who get the flu are at risk for giving birth to significantly underweight babies.

"It shows again that when you prevent flu in a pregnant woman, you benefit the mother, you benefit the infant, and we think this also shows that you benefit the fetus and the growth of the fetus," he said.

In yet another study of pregnant women in Bangladesh, Emily Henkle, from the Bloomberg School of Public Health at Johns Hopkins University in Baltimore, wanted to determine the rate of flu infection in their infants.

Henkle, part of Steinhoff's team, found high rates of flu among infants younger than 6 months whose mothers had not been vaccinated.

"In the first six months of life, in this setting, in the tropics, 25% of the infants had flu infection," Steinhoff said. "It's a higher rate of infection than has been reported anywhere else."

In North America, about 10% of infants have flu in the first six months of life, he added.

Another report scheduled for presentation at the meeting examined the response of health-care workers to the call for flu shots. Researchers from Children's Mercy Hospital in Kansas City, Mo., surveyed a random group of doctors, nurses and other employees about their knowledge of flu vaccine and their attitudes and beliefs about having themselves and their children vaccinated.

The researchers found high vaccination rates in the hospital, but gaps in flu knowledge and vaccine safety in all groups. Doctors were more comfortable than others with a mandatory vaccine policy, they said.